<?php

$thismonth = date('m');

$thisyear  = date('Y');

$startDay = $thisyear . '-' . $thismonth . '-1';

$endDay   = $thisyear . '-' . $thismonth . '-' . date('t', strtotime($startDay));

$b_time       = strtotime($startDay);

$e_time       = strtotime($endDay);

<?php

$thismonth = date('m');

$thisyear  = date('Y');

if ($thismonth == 1) {

    $lastmonth = 12;

    $lastyear  = $thisyear - 1;

} else {

    $lastmonth = $thismonth - 1;

    $lastyear  = $thisyear;

}

$lastStartDay = $lastyear . '-' . $lastmonth . '-1';

$lastEndDay   = $lastyear . '-' . $lastmonth . '-' . date('t', strtotime($lastStartDay));

$b_time = strtotime($lastStartDay);

$e_time = strtotime($lastEndDay);